Differentiation: A Central Topic in Developmental and Cell Biology

MyoD/myogenin   genes and neural key genes (e.g., achaete scute-C, neurogenin), are switched on which control entire sets of subordinate effector genes. In multiplying cells "cell heredity" based on an epigenetic cellular memory enables transmission of the cell type determining program from parental to daughter cells. This memory can be based on autocatalytic self-activation of cell type specific selector genes and on the enduring action of gene groups such as the Polycomb and thrithorax complexes that code for proteins which bind to DNA sequences called cellular memory modules. These modules confer permanent accessibility (potentiation) or inaccessibility (silencing) upon many different gene loci on the chromosomes.